This invention pertains to fluid system augmentation (particularly pertinent to aircraft type hydraulic systems) and more particularly to augmentation systems of a bootstrap type wherein augmentation is provided to valve controlled power actuators by the addition of a jet pump or ejector in combination with means to use the aiding load generated pressure differential in the power actuator.
While the schematics and sketches shown and discussed herein are directed to aircraft type servo applications, the teachings of this invention apply equally well to any valve controlled actuator which sees both aiding and resisting loads. FIG. 1 is illustrative of a typical prior art aircraft power actuator system showing a conventional single-stage single system servoactuator hydraulic subsystem schematic. System pressure and flow is diverted to one side of the actuator by commanding the force motor 5 to drive the main control valve (MCV) 7 in the appropriate direction. If a large aiding load were applied on the actuator at F, the system pump would have to supply sufficient flow in chamber B to avoid cavitating that side of the power actuator since the aiding load supplies the motive force to deflect the control surface.
One alternative is to restrict the flow out of chamber A which, of course, slows down the actuator. A further alternative known in the art is to short circuit chamber A to chamber B when chamber A pressure exceeds the pressure in chamber B. This is done either directly or through the control valve by connecting chamber A to chamber B with a check valve allowing flow from A to B but not from B to A. Since the MCV directs system pressure and flow to either chamber, chamber A may become the pressure chamber and chamber B return, so there has to be another line interconnecting the chambers with a check valve which allows flow from chamber B to chamber A but not from A to B. These check valves are shown in two alternate schemes in FIGS. 2 and 3 as valves 9 and 11 with associated plumbing. These valves are ordinary check valves and are sometimes referred to in the aircraft industry as "run-around" check valves when installed as indicated to avoid cavitating the pressure-side chamber of a power actuator experiencing high velocity rates. They will be referred to hereinafter as load recovery valves (LRV) to avoid confusion with other check valves in the circuit.
The dotted line curve of FIG. 9 shows the comparative actuator velocity, expressed as a percent of no load steady state velocity, against the percent of maximum load with the use of the load recovery valves as compared to the solid line without the load recovery valves. While this velocity increase is substantial, it is experienced only with an aiding load above 20% maximum. While the load recovery valves provide a definite flow enhancement, it is experienced only over a narrow part of the loading regime and is inadequate, in most cases, by itself to allow reduction in the system pump size.
It is an object of the present invention to further increase the flow enhancement and to spread the enhancement over a greater portion of the actuator load regime so as to permit a reduction in the system pump size and as a result to reduce the heat generated by the smaller pump and reduce system weight by reducing the size of the pump and the associated plumbing. It is an alternate object of the invention to augment flow so as to permit increasing actuator rates which is particularly applicable on redesigns or modifications of existing aircraft.